How to use "prefetch" on llblgenprodatasource
Joined: 28-Dec-2010
Hi
We encountered one problem which lead to seldom use the llblgenprodatasource. E.G
<llblgenpro:LLBLGenProDataSource2 ID="regulationBaseSource" runat="server" CacheLocation="Session"
AdapterTypeName="BusinessObjects.Adapter.DatabaseSpecific.DataAccessAdapter, Enhesa.BusinessObjects.Adapter"
DataContainerType="EntityCollection" EntityFactoryTypeName="BusinessObjects.Adapter.FactoryClasses.RegulationBaseEntityFactory, BusinessObjects.Adapter"
LivePersistence="true" EnablePaging="true" >
<SelectParameters>
<asp
arameter Type="String" Name="CountryCode" DefaultValue="BE" />
<asp arameter Type="String" Name="RegionCode" DefaultValue="_countrywide" />
</SelectParameters>
</llblgenpro:LLBLGenProDataSource2>
Every llblgenprodatasource only focus on one entity, here is RegulationBaseEntity.
But in many situation, we should present many information from all kinds of entities which have relationships each other. Such as: from r in linqMetaData.RegulationBase.WithPath(a=>a.Prefetch<RegulationTextEntity>(b=>b.RegulationText).Prefetch<RegulationCourntryRegion>(b=>b.RegulationCountryRegion>) select new RegulationInfo { RegID = r.RegID, RegTitle = r.RegulationText.single(n=>n.languagecode == "en").RegTitle, CountryCode = r.RegulationCourntryRegion.CountryCode, RegionCode = r.RegulatitonCountryRegion.RegionCode, }
As usual, we directly use the "objectdatasource" to provide the datasource of "RegualtionInfo" above.
Our difficult problem is that we didn't know how to use the pretch way on llblgenprodatatsouce. e.g, regulationDatasouce above, is a llblgenprodatasource. Becasuse regulationDatasouce was only used for RegulationBase, I want to this datasouce how to pretch RegulationText and RegulationCountryRegion, then GridView can present information from RegulationBase, RegulaitonText, RegulationCountryRegion with regulationDatasouce.
Best regards
Joined: 28-Dec-2010
Joined: 02-Nov-2007
Joined: 02-Nov-2007
Joined: 02-Nov-2007
Joined: 02-Nov-2007
Walaa wrote:
For first level prefetchPath, the following should work:
'<%# DataBinder.Eval(Container.DataItem, "Customer.Name")%>'Assuming you were fetching Orders and prefetching the Customers.
Otherwise you may create a custom Property in the fetched entity to return back the dete you want to display from the prefetched entity.
No. that just doesn't work at all. If it did, we wouldn't need this thread.
As I said, this only works if you recompile your LLB Adapter with [Browsable(true)] on the Customer related collection. It might have worked 3 years ago though.
Creating custom properties for the bazillion things we need isn't an option. Not all databases are as simple as Northwind
We have 150 tables and rarely, if ever, can we get data from just one table. That is precisely the reason we need to use LLB objects with their paths in aspx controls.
Design-wise, in web applications it can be costy to fetch entities with multiple prefetchPaths to display data from more than one table.
Thus normally I'd recommend using flat lists (TypedList or DynamicList). As these are more light weight and right to the point. This of course comes at the cost of some code wiring in case you want to save back edited data. As you will need to map the edited row to an entity object to be saved.
Otherwise you should alter the browsable attribute as you have said, but wait.. There's a setting for that.
You might have missed this thread: http://www.llblgen.com/tinyforum/Messages.aspx?ThreadID=18913&StartAtMessage=0𙼳
Joined: 02-Nov-2007
Joined: 02-Nov-2007
Joined: 02-Nov-2007
Joined: 02-Nov-2007
Joined: 02-Nov-2007
I'm a bit lost about what exactly the issue is currently, please help me with this -> Prefetch paths issue, that's sorted, correct?
FirstOrDefault is implemented, I don't know why you thought it wasn't? (it works similar to First(), and will return null if the entity wasn't found).
To avoid null's, test for them, there's no other way around it, I'm afraid.
Joined: 02-Nov-2007
Otis wrote:
I'm a bit lost about what exactly the issue is currently, please help me with this
Bottom line: I think I can solve our problems by using specialized custom property implementations. Below is a fuller description of what is happening.
Otis wrote:
FirstOrDefault is implemented, I don't know why you thought it wasn't? (it works similar to First(), and will return null if the entity wasn't found).
FirstOrDefault() "FirstOrDefault. This method has the same result as First: the 'Default' part isn't implemented: if there is no result, you won't receive any result but null. If First is called on a set which is empty, null is returned "
So I can use it but it returns null. I think I might have been looking for DefaultIfEmpty(T) where I could put a null object that would avoid exceptions. I'll try it, but I don't think this is necessarily a problem for me if my custom properties implementation handles nulls.
Otis wrote:
To avoid null's, test for them, there's no other way around it, I'm afraid.
That is why I think I can't effectively use the Eval syntax to get properties from prefetch or subpaths of an entity. Null Exceptions at runtime will be a recurring problem.
The wish is to use EntityCollections with prefetch paths in LLBLGenProdataSource2s in conjunction with a grid. This is especially where the data is modified as the LLB DS kindly manages it all for us and lets us do a one line commit. We use ASPxGridView, but I think that is immaterial.
So the options are:
- project to a flat plain class which needs lots of work to commit to the database
- use Eval("Entity.PrefetchPath.property") which I haven't tried to commit yet
- Create Custom Properties on the Entity which commit just fine with the right implementation of the custom property setter
So in a write situation, in order to use e.UoW.Commit(adapter) we can use Custom Properties. I haven't tried the Eval approach in this situation (yet) as I doubt it will work for the reasons below and maybe others.
Custom Properties seem easy enough except when the related entity is null. Then the designer for the grid breaks as it gets an exception when checking the property. Commits also fail as there is no collection to update, hence the need implement this in the setter. I think I can fix this by modifying my custom properties to handle this situation and am currently working on that approach.
Using the Eval approach above throws an exception at runtime when the .PrefetchPath or SubPath is null. This means I can only use it if related entities return a Null Object (i.e. an entity with default data only) when there is no data to return. I think, as you point out, this is a non-starter.
Therefore, I am moving ahead with Custom properties for both read and write needs for databound controls. This eliminates the need to create a projection in most cases where all we want is a flat set of properties for the binding.
I am also investigating how to use the PrefetchPathToUse property on the LLB DS. Once I understand what it does, this might give me a better way to architect our views using many more databound controls, each of which bind to a specific prefetch path. That sounds pretty wonderful to me if that is what it lets me do. (UPDATE: This is nonsense. Sorry. I don't think PrefetchPathToUse is useful when you have already added them in the performSelect handler)
Joined: 28-Dec-2010
Hi All,
I am sorry to back so late. I am often be late by busy work and forget to give out feeback asap.
I explain neilx what he want to do use llblgenpro prefetch. I did a successful expirement on Northwind.
View code:
<div> <dxwgv:ASPxGridView ID="ProductsDetails" AutoGenerateColumns="false" runat="server" DataSourceID="productsDS" KeyFieldName="ProductId"> <Columns> <dxwgv:GridViewDataColumn FieldName="ProductId"></dxwgv:GridViewDataColumn> <dxwgv:GridViewDataColumn FieldName="ProductName"></dxwgv:GridViewDataColumn> <dxwgv:GridViewDataColumn FieldName="SupplierId"></dxwgv:GridViewDataColumn> <dxwgv:GridViewDataColumn FieldName="CompanyName"></dxwgv:GridViewDataColumn> <dxwgv:GridViewDataColumn FieldName="Address"></dxwgv:GridViewDataColumn> <dxwgv:GridViewDataColumn FieldName="Phone"></dxwgv:GridViewDataColumn> <dxwgv:GridViewDataColumn FieldName="OrderDetailsUnitPrice"></dxwgv:GridViewDataColumn> <dxwgv:GridViewDataColumn FieldName="Quantity"></dxwgv:GridViewDataColumn> <dxwgv:GridViewDataColumn FieldName="Discount"></dxwgv:GridViewDataColumn> <dxwgv:GridViewCommandColumn> <EditButton Visible="true"></EditButton> </dxwgv:GridViewCommandColumn> </Columns> <SettingsEditing Mode="Inline" /> </dxwgv:ASPxGridView> <llblgenpro:LLBLGenProDataSource2 ID="productsDS" runat="server" AdapterTypeName="DevExpress.Adapter.DatabaseSpecific.DataAccessAdapter, DevExpress.Adapter" CacheLocation="Session" DataContainerType="EntityCollection" EntityFactoryTypeName="DevExpress.Adapter.FactoryClasses.ProductsEntityFactory, DevExpress.Adapter" EnablePaging="True" LivePersistence="true"> <SelectParameters> <asp:P arameter Type="Int32" Name="OrderId" DefaultValue="10248" /> <asp:P arameter Type="Int32" Name="ProductId" DefaultValue="11" /> </SelectParameters> <UpdateParameters> <asp:P arameter Type="Int32" Name="OrderId" DefaultValue="10248" /> <asp:P arameter Type="Int32" Name="ProductId" DefaultValue="11" /> </UpdateParameters> </llblgenpro:LLBLGenProDataSource2> </div>View BackGround Code protected void Page_Load(object sender, EventArgs e) { IPrefetchPath2 path = new PrefetchPath2((int)EntityType.ProductsEntity); path.Add(ProductsEntity.PrefetchPathSuppliers); path.Add(ProductsEntity.PrefetchPathOrderDetails); productsDS.PrefetchPathToUse = path; }
ProductsEntity CustomProperties code namespace DevExpress.Adapter.EntityClasses { public partial class ProductsEntity { public string CompanyName { get { return HasNoSuppliers() ? null : Suppliers.CompanyName; } set { Suppliers.CompanyName = value; } }
public string Address
{
get { return HasNoSuppliers() ? null : Suppliers.Address; }
set { Suppliers.Address = value; }
}
public string Phone
{
get { return HasNoSuppliers() ? null : Suppliers.Phone; }
set { Suppliers.Phone = value; }
}
public decimal OrderDetailsUnitPrice
{
get { return HasOrderDetails() ? decimal.Zero : OrderDetails[0].UnitPrice; }
set { OrderDetails[0].UnitPrice = value; }
}
public short Quantity
{
get { return HasOrderDetails() ? short.MinValue : Convert.ToInt16(OrderDetails[0].Quantity); }
set { OrderDetails[0].Quantity = value; }
}
public float Discount
{
get { return HasOrderDetails() ? 0 : OrderDetails[0].Discount; }
set { OrderDetails[0].Discount = value; }
}
private bool HasNoSuppliers()
{
if (Suppliers == null)
return true;
else
{
return false;
}
}
private bool HasOrderDetails()
{
if (OrderDetails == null)
{
return true;
}
if (OrderDetails.Count() == 0)
{
return true;
}
return OrderDetails.Count() == 0;
}
}
}
Then my test result
How superful function of llblgenpro !!! "ProductsEntity" pretech "SuppliersEntity" and "OrderDetailsEntity", and there is so less code to present 3 tables fields. I can upate any fields of 3 entities or tables at one time. In "old period", we often use objectdatasource and many customersizing code to implement to view or update informtation of mutli -tables.
LLBLGenProDataSource2 prodcutDS, seemingly, only responsible for ProductsEntity. But the prefetch change everything. productDS can deal with ProductsEntity, SuppliersEntity and OrderDetailsEntity.
Now, I think we have been left from dark and see dawn from now on. You discussion help me so much. Thank you very much.
Hi neilx, How do you think? My solution colse to your expectation, is it right?